The invention relates to a gas bag for a vehicle occupant restraint system.
The shape of an inflated gas bag may be influenced and controlled by internal tethers. Each of these tethers is sandwiched between two superimposed plies of fabric to which it is stitched, or woven by a special weaving technique. In any case, such internal application of tethers involves considerable production time and costs. When the tethers are secured to the plies of fabric by seams, these seams need to be implemented through the inflation port of the gas bag. Weaving the internal tethers to the superimposed plies of fabric necessitates a special weaving technique which is highly complex.
The invention provides a gas bag for a vehicle occupant restraint system, the internal tether means of which may be applied with minimum production time and costs. In accordance with the invention the internal tether means are formed by at least one seam through the plies implemented with a thread slack. Such a seam having thread slack may be implemented from without into the superimposed plies of fabric which may thus be spread out flatly on top of each other in applying the seam and enabling a conventional stitching technique to be employed.
In the folded condition of the gas bag the thread slack of the seam forms loops arranged between the plies of fabric or on the outer side of one of the plies of fabric. On inflation of the gas bag the thread slack is pulled out until the loops are eliminated. The plurality of tensioned threads in the interior of the gas bag act like a tether which limits the expansion of the gas bag in the direction of extension of the threads. Since applying a seam with thread slack involves little outlay in production, engineering novel configurations of the gas bag now comes into consideration which would be too complicated with conventional tethers. It is thus now possible with no great outlay to apply a number of seams with thread slack acting as tether means on the gas bag which on deployment and expansion of the gas bag control the shape thereof up into its rim portions.
Particularly suitable types of seam are the double lock stitch seam and the double chain stitch seam. In both cases the thread. slack is preferably formed in the underthread.
In a head bag a sufficient, possibly constant, gas bag thickness needs to be provided over the entire restraint portion, i.e. the portion on which impact of a vehicle occupant is to be reckoned with. Currently the thickness of the individual restraint chambers of the head bag is defined by the spacing of seams defining the chambers in the bag. These seams directly join the plies of fabric. This technique usually represents a compromise between gas bag thickness, volume and probable place of impact of the head of a vehicle occupant which on no account must impact a nip seam. However, it is usually not possible to do without nip seams in a restraint portion.
Due to the mandatory requirement of ensuring that the occupant""s head does not impact a nip seam, an adequate gas bag thickness needs to be made available throughout all of the restraint portion to permit achieving the same restraint everywhere. The bracing and stiffening of the gas bag offered by the chambering due to nip seams should be retained or achieved by other means.
In any case, however, applying tethers internally involves a considerable production outlay. When the tethers are seamed to the plies of fabric, these seams need to be implemented through the inflation port of the gas bag. Spot fastening the tethers at both their ends has, on the one hand, a negative effect on achieving a constant thickness of the restraint portion and, on the other, high forces materialize at fastening points in the gas bag fabric which in a restraint situation could result in the gas bag being damaged. Weaving the internal tethers to the superimposed plies of fabric necessitates a special weaving technique which is highly complicated.
Using the inventive concept of tethers formed by seams with thread slack allows the bag to have a substantially constant thickness throughout all of the restraint area, whereby the gas bag can be fabricated simply and with no high handling requirement in production.
A seam having thread slack may be applied from the outside into the superimposed plies of fabric which may thus be spread out flatly on top of each other in applying the seam or seams and enabling a conventional stitching technique to be employed.
It is particularly advantageous in the folded condition of the gas bag to arrange the loops of the thread slack between the plies of fabric since this excludes any tangling of the loops due to external effects whilst likewise preventing the gas bag material possibly being damaged by the pull-through of the thread slack through the fabric during inflation of the gas bag.
In a further aspect of the invention for configuring the seam during stitching a spacer is temporarily arranged between the two plies of fabric of the gas bag to obtain a seam implemented with an extremely large slack. This spacer has practically the desired thickness of the inflated gas bag and is removed after stitching. The thread slack is thus achievable without any complicated stitching techniques. The slack thread of the seam is thus located, with the gas bag folded, in the interior of the gas bag and is not tensioned until the gas bag is deployed. In this way a tether function distributed over a large area is achievable without using many individual nip seams which would affect the restraining effect. The seam may also assume the chamber defining function. After having stitched the tether seam the rim seam of the gas bag may be fabricated with a seam material holder as hitherto.
In accordance with a further advantageous embodiment of the invention the tether means is configured as a tether structure comprising in all at least three fastening points on the two plies of fabric. For one thing, the higher number of fastening points reduces the load exerted by the tether means on the gas bag fabric in a restraint situation, and for another, a wealth of possibilities for configuring the shape of the gas bag is now made available by the choice in configuring the tether structure and the arrangement of the fastening points, this permitting engineering, more particularly, the tightening of the lower edge of a side gas bag. The tether means itself may be prefabricated outside of the gas bag to reduce the production outlay.
To advantage the tether structure is configured V- or X-shaped. A structure arranged V- or X-shaped in the inflated gas bag is simple to fabricate and to process with great freedom of arrangement in the gas bag.
In another advantageous embodiment the tether means is formed from a section in which folds of the fabric parts of the gas bag are stitched to each other. In this aspect no additional components are needed and the possibilities of configuring the shape of the gas bag are many and varied. Compartmenting the gas bag into chambers is also achievable.
In accordance with yet another advantageous embodiment the tether means is formed from a piece of material extending between the fabric parts, this piece of material preferably being circular. A piece of material may be secured to a larger surface area than a conventional tether to reduce the load on the gas bag fabric. This embodiment too, offers a wealth of possibilities of shaping the gas bag.